The present invention generally relates to prosthetic implants and more particularly to a prosthetic wrist implant having a geometry that closely matches that of a natural wrist, which is adjustable during the implantation process so as to more closely approximate the motion of a natural wrist, and which achieves good stability through better apposition and compression with the remaining carpal bones.
With reference to FIG. 1 of the drawings, the dorsal side of the bone structure of a patient""s left hand and wrist is illustrated in conjunction with the radius 2 and the ulna 4. The bone structure includes a carpal bone complex 6 having a scaphoid 8, a lunate 10, a triquetrum 12, a pisiform 14, a trapezium 16, a trapezoid 18, a capitate 20 and a hamate 22. It will be appreciated that the scaphoid 8 and the lunate 10 bones articulate with the radius 2 during the movement of the wrist.
In a variety of wrist disorders, patients may experience discomfort, pain and difficulty in moving the wrist. Prior surgical treatment of this condition involved fusion to inhibit movement of the scaphoid 8 and the lunate 10 bones relative to the radius to thereby alleviate pain in the patient""s wrist. This procedure, however, leaves the patient without motion in their wrist and thereby severely restricts the use of their wrist. Modernly, prosthetic wrist implants have been developed to provide a pair of artificial bearing surfaces for the wrist. Several of the prior wrist implants have suffered from drawbacks including limited range of motion and excessive bone resection. Others still provide proper motion only when aligned in an extremely precise manner relative to the carpal bone complex 6. While various jigs and fixtures may be employed to aid in the locating and forming of a hole in the distal portion of the carpal bone complex 6 for receiving a carpal implant, these devices typically do not completely eliminate the possibility of error in the alignment and forming of the hole.
Accordingly, there remains a need in the art for an improved prosthetic wrist implant that provides improved support and strength for the distal portion of the carpal bone complex 6 and which has a bearing surface whose orientation is changeable after implantation to provide the implanted prosthetic wrist with a range of motion that mimics the range of motion of a natural wrist.
In one form, the present invention provides a prosthetic wrist with a carpal implant that includes a body, a lateral flange and a medial flange. The body has a stem that is arranged along an axis and which is configured to be implanted in a capitate bone in a human wrist. The lateral flange, which includes a lateral bone abutment surface that is configured to be abutted against an ulnar side of a hamate bone in the human wrist, is coupled to the body and extends therefrom such that at least a portion of the lateral bone abutment surface is skewed to the axis of the stem by an angle of less than 90 degrees. The medial flange, which has a medial bone abutment surface that is configured to abut against a radial side of a trapezium bone and a portion of a resected scaphoid bone of the human wrist, is coupled to the body and extends therefrom on a side opposite the lateral flange.
In another form, the present invention provides a method for implanting a prosthetic wrist implant between a patient""s radius and carpal bone complex. The method includes: providing a carpal implant including a body, a lateral flange and a medial flange, the body having a stem that is arranged along an axis, the lateral flange being coupled to the body and extending therefrom, the lateral flange having a lateral bone abutment surface, at least a portion of the lateral bone abutment surface being skewed to the axis of the stem by an angle of less than 90 degrees, the medial flange being coupled to the body and extending therefrom on a side opposite the lateral flange, the medial flange having a medial bone abutment surface that is skewed to the axis of the stem by an angle of less than 90 degrees, each of the lateral and medial flanges having a bone screw aperture formed therethrough; resectioning a proximal portion of the carpal bone complex; forming an opening in the capitate bone that lies along an axis that is generally coincident with the axis of the capitate bone; forming a pair of securing apertures into a distal portion of the carpal bone complex, one of the pair of securing apertures being formed in the hamate bone; securing the carpal implant to the distal portion of the carpal bone complex such that the stem is at least partially disposed in the opening in the capitate bone and engaged to the capitate; providing a first screw and a second screw, the first and second screws being appropriately sized to the pair of securing apertures and the bone screw apertures; placing the first screw through the bone screw aperture in the lateral flange and the securing aperture in the hamate bone and securing the first screw to the hamate to bring the lateral bone abutment surface into abutment with an ulnar side of a hamate bone; and placing the second screw through the bone screw aperture in the medial flange and the other securing aperture in the distal portion of the carpal bone complex and securing the second screw to the distal portion of the carpal bone complex to bring the medial bone abutment surface into abutment with a radial side of the distal portion of the carpal bone complex.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.